1. Technical Field
The present invention relates to an image reading apparatus and a semiconductor device.
2. Related Art
A complementary MOS (CMOS) process has high convenience because of being allowed to form a logical circuit and an analog circuit on the same IC chip. Thus, recently, various technologies relating to the CMOS process have been developed. An imaging sensor is no exception. An imaging sensor by the CMOS process (CMOS imaging sensor) instead of a CCD imaging sensor has been actively developed.
In the related art, as a circuit configuration of a CMOS imaging sensor, a column output circuit (referred to as a column processing unit below) is known. In the column output circuit, a signal is read from a photoelectric conversion unit (pixel unit) including a light receiving element, in a column direction. According to this configuration, parallel processing by a plurality of column processing units which form a pair for each light receiving element can be possible. Thus, it is possible to lower a data rate of each of the column processing units, and to reduce a noise level. Further, each of the column processing units includes a correlated double sampling (CDS) circuit, and thus it is possible to cancel a noise generated in the photoelectric conversion unit (pixel unit). Output magnification of a signal to be read may be also arbitrarily set depending on a ratio of capacitance of the CDS circuit and feedback capacitance. As the column processing unit, a source-grounded type amplifier is employed in many cases. This is because an amplifier is required for each column processing unit and thus a source-grounded type amplifier which may be mounted with an area smaller than that of a differential amplifier is more appropriate for reducing the size, than the differential amplifier.
The source-grounded type amplifier has a problem in that a power supply rejection ratio (PSRR) which is a ratio of the increased or decreased amount of an input offset voltage to fluctuation of a power source voltage is worse than that in the differential amplifier. Considering this circumstance, for example, a technology (solid state imaging device) for solving this problem is proposed in JP-A-2005-252529. In detail, a current value of an amplifier in a column processing unit is set to be constant, levels of a power source and the ground are maintained to be normally constant, and thus it is possible to improve the PSRR. According to the descriptions (for example, paragraph [0005], FIG. 4, and the like) of JP-A-2005-252529, it is supposed that output voltage characteristics are substantially proportional to illumination.
However, in the solid state imaging device of the related art, which is described in JP-A-2005-252529, there is a problem in that removing an offset voltage due to a source-grounded type amplifier of a column processing unit is difficult, and thus a dynamic range becomes narrower, and reading an image with high accuracy is not possible.